The Difference Between Shampoo and Soap

If you ask any of us at Upfront about our “soap bars”, we might get a little prickly with you. It’s not soap! They’re totally different! Of course, we have the knowledge and experience to know WHY they’re different, that the average consumer might not have. To be fair, the landscape of personal care products has changed drastically over the past 30 years. These days shampoo comes in a bar, and hand soap can be rich & foamy like shampoo. Both can be scented or unscented, coloured or clear. So why can’t we mix and match? Here’s why you should think twice about using that yummy peach scented hand soap on your hair in a pinch. 

Up until the 1930’s, it was standard practice to use bar soap in your hair. Something many people may not realize is that what we consider soap these days is actually detergent. What’s the difference? Traditionally “soap” is made by combining animal or vegetable fat with an alkaline solution, such as lye. This means “soap” can be made of entirely natural ingredients. In the modern age, we’ve industrialized the process. This means most soaps today are made with man-made surfactants, referred to as “detergents”, in combination with other chemicals that make the product look and smell nice, as well as perform better. These may be vegetable or mineral oils, or they may also be synthetic compounds. 

The most common detergent used in personal care products is sodium lauryl sulfate, or SLS. It’s well known for the rich lather it creates. In the past, this blog has denounced the use of SLS and other sulfates, which you can read hereDetergents and soap work in the same way: one end of the surfactant molecule attaches itself to the oil or dirt in your hair & scalp, while the other end of the molecule adheres to the water. When you rinse your hair, all the yuck is washed away with it. The issue with SLS is, it works almost too well. The detergent can’t tell the difference between the oil that’s building up in your hair and the natural oil needed for protection and shine. So much nourishment gets washed down the drain.

Having said that, even shampoos made with SLS are better for your hair than “soap”. Shampoo takes the SLS factor into account, meaning shampoo formulas contain a lower percentage of the surfactant than soap formulas, making it more easily rinsed off. It’s formulated with additional ingredients that undo the damage the detergent can inflict, like a conditioner of some sort to restore shine and combat frizz, and perhaps oils and proteins to make hair stronger over time. Shampoos made to match the pH balance of your scalp are increasingly common too. Despite the harshness of the SLS, shampoo is formulated for hair care specifically, unlike, say, hand soap or shower gel. 

That’s not to say that the only shampoo worth having is one that uses SLS. Of course that’s not the case! Many plant-based detergent alternatives to SLS exist, which are much milder. One common method is to use fatty alcohols, such as stearyl, cetyl, or cetearyl alcohol. It may sound counterintuitive on account of how drying alcohol is, but fatty alcohols actually work in the opposite way; they provide hydrating properties which absorb and lock in moisture and keep hair from drying out. At Upfront, we use three different coconut-based surfactants in place of traditional detergent: SCI, SLSa, and Coco Betaine. Each one is much more mild than traditional detergents, but the combined power of the three of them makes for a rich lather that rivals any detergent-based shampoo, while still being gentle enough for even the most sensitive scalps!

The main takeaway from all this, is that there’s a vast difference in the chemical makeup between soap and shampoo. Shampoo is formulated especially for hair, either with less detergent than soap, or with a detergent-free surfactant. It also comes packed with additional hydrating, nourishing ingredients for healthier hair over time. Shampoo is made to be easily rinsed, while soap may leave a residue. In a pinch, you could use shampoo on your body, though it would likely take a little more rinsing; you certainly wouldn’t want to go in the other direction. Keep that body wash or hand soap away from your hair!


Photo by Townsend Walton on Unsplash

1 comment

  • Hugo Montenegro

    Thanks for the great information on the different chemically makeup of soap compared to shampoo.
    Very informative and interesting in clearing any doubts.

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